Spark plug and electrodes therefor



y 9, 1940- c. H. COLEMAN SPARK PLUG AND ELECTRODES THEREFOR Filed Feb.25, 1939 Patented July 9, 1940 UNITED STATES PATENT OFFICE 1 Claim.

This invention relates to improvements in igniting devices for internalcombustion engines.

The present invention has for its primary ob ject to provide an improvedigniting device or spark plug in which the electrodes are made ofcommercially pure copper which has been hardened according to myimproved process.

Another object of the invention is to provide an improved spark plug orinternal combustion engine igniting device having hardened commerciallypure copper electrodes which are secured in the device in such a mannerthat they may be replaced when, as and if necessary, so that the plugproper may be used indefinitely, the only repairs or replacementsnecessary being the occasional replacement of the electrodes thereof.The invention will be best understood from a consideration of thefollowing detailed description taken in connection with the accompanyingdrawing forming part of this specification, with the understanding,however, that the invention is not to be confined to any strictconformity with the showing of the drawing but may be changed ormodified so long as such changes or modificao tions mark no materialdeparture from the salient features of the invention as expressed in theappended claim.

The accompanying drawing illustrates a spark plug having electrodesformed of commercially pure copper hardened in accordance with myimproved process and showing the manner in which such electrodes may beinstalled for easy replacement.

In the drawing:

Fig. 1 illustrates a spark plug constructed in accordance with thepresent invention, the same being shown in side elevation.

Fig. 2 is a vertical longitudinal section through the same.

In setting forth the present invention, a description will first begiven of the structure of the spark plug illustrated in the drawingafter which a statement will be made of the process employed forhardening the copper from which the electrodes are made. A

The numeral I generally designates the shell of the plug in which theupper portion is of polygonal contour, as indicated at 2, to facilitatethe application of a wrench thereto whereby the threaded reduced lowerend portion 3 may be secured in or unthreaded from the spark plug holein the head of an internal combustion englne. Below the polygonal shapedportion 2 of the shell, the shell is provided with the encircling ribsor flanges 4 which serve to dissipate heat by presenting an increasedarea of the body to the air.

The shell I is of the usual hollow form and is interiorly threaded atits upper end to receive a bushing 5 by means of which the insulationsleeve 6, of porcelain or other suitable insulation material, ismaintained in position. This sleeve has the usual longitudinallyextending passage therethrough, as indicated at l, but this. passagethrough a portion of its length at the lower end of the sleeve is ofreduced diameter while at its upper end it is enlarged to receive themetal liner 8 which is interiorly threaded and in which is adapted to beengaged the hollow binding nut 9, the inner end portion of which isprovided with a pocket I l! for the purpose hereinafter described. Thisnut is formed to have the usual wire connection of the ignitionmechanism made therewith. A suitable thin copper washer may beinterposed between the top edge of the liner 8 and the binding nut 9, asindicated at H.

The lower portion of the insulation bushing or sleeve 6 has an enlargedwaist which is clamped between the bottom of the shell and the bushingand in order to prevent leakage, suitable copper washers I2 and I3 areinterposed between the sleeve and. the bushing and shell, as shown.

The lower edge of the reduced portion 3 of the shell is provided with alongitudinally extending threaded bore and threadably secured in thisbore is one end of the ground electrode I4. By this means, thiselectrode may be removed and a new one substituted when necessary. Thenumeral l5 designates the central electrode of the plug which, as shown,has a thin or reduced lower end portion l6 and a larger upper endportion ll, which portions respectively position in the reduced lowerportion of the passage 1 of the insulation sleeve and in the largerupper portion thereof in the manner shown. The upper end of theelectrode [5 is frictionally held in the pocket [0 of the binding nut,so that when this nut is released from the liner 8 and removed, thecentral electrode may also be withdrawn to be replaced by a new one.

The electrodes l4 and I5 are formed from commercially pure copper whichhas been hardened by the following process, which process does notinvolve either alloying or working the metal. The copper selected is ofthe purest commercial grade obtainable, such copper normally averaging99.98% purity. The impurities therein consist of lead which approximates.0l5%; silver, aluminum and magnesium approximating .0001%; calcium andsilica approximating .001%. These impurities were determined byspectrographic analysis, in a specimen selected for use in the presentinvention and for hardening as hereinafter described, the copper,constituting by difference, 99.98%.

In treating the selected copper according to the present process, themetal is first reduced in temperature to slightly below the freezingpoint of water or, in other words, to 32 F. or slightly below, and afterbeing reduced to such temperature, it is then immersed in a bath of beeftallow which has been heated to a temperature of approximately 240 F.,the immersion being for a period of approximately seconds more or lessaccording to the size or thickness of the piece of metal treated.Immediately following this step, the metal is transferred to a soapsolution which is maintained at boiling point. This soap solution may bemade from any suitable laundry or other type of soap and has a densityof approximately 1.009. The metal is allowed to remain in this boilingsoap solution for approximately 30 seconds. Following this last step,the metal is removed and thoroughly dried and allowed to come back toapproximately room temperature or from between 60 and 80 F. It is isthen subjected to a second chilling step wherein the temperature isreduced to approximately 10 below zero. After this desired temperaturereduction has been obtained in the metal, it is again immersed in thehot tallow solution, the temperature of which has been raised toapproximately 280 F. and allowed to remain approximately 20 secondsafter which its is transferred to the boiling soap solution for 30seconds and is subsequently thoroughly dried and allowed to return tonormal or room temperature preparatory to car-- rying out the third stepof the operation. Repetition of the last described series of steps ismade as many times as may be desirable to bring about the desiredhardness of the metal and with each repetition of the three steps ofchilling, immersion in hot tallow and then in the soap solution, thetemperature of the tallow is raised about The first rise is from 240 to280 F. and after that, the 10 increases are made until the desireddegree of hardness is attained. Following the second series of steps,the reduction in the temperature of the metal is not increased. Themetal is reduced each time to approximately 10 below zero, and themaximum temperature for the tallow is approximately 400 F.

It has been found that in the foregoing process, the reaction occurringin rapidly changing the metal from the chilled condition to a highlyheated condition in hot tallow or in any other similar fluid by means ofwhich the temperature can be rapidly raised out of contact with the air,has the effect of hardening and toughening the metal without permittingany oxidation to occur.

Commercially pure copper treated according to the above describedprocess may be hardened to a degree where it may be made into spark plugterminals which will stand the high degrees of heat occurring in aninternal combustion engine cylinder. Such tempered or hardened copper isalso employed for making the shell and bushing portion of the plug andhas been found to dissipate heat more rapidly than steel or other metalsused for this purpose and thereby prevent overheating of the points andpreignition.

From the foregoing, it will be apparent that the spark plug structure,particularly described, is novel in the provision of means for removaland replacement of the electrodes and is also novel in the use of thehardened copper electrodes. The use of such electrodes will materiallycheapen the production cost of such plugs as the material for the sameand the process of hardening the material is relatively inexpensive ascompared with the metals at present used for electrode points.

What is claimed is:

A spark plug, comprising a shell, an insulation body supported in andextending through the shell, said insulation body having a passageextending longitudinally therethrough, a ground electrode secured to oneend of the shell in spaced relation with said insulation body, aninteriorly threaded collar secured in the insulation body at the endthereof remote from the ground electrode, a terminal body threadablysecured in said collar, a central electrode having an end secured tosaid terminal body and extending therefrom through the passage of theinsulation body and terminating in close proximity to said groundelectrode, said central electrode being designed to be withdrawn throughthe collar supporting end of the insulation body with said terminalbody, and said electrodes being formed or" hardened high temperatureresisting copper.

CLAUDE H. COLEMAN.

